1. Field of the Invention
The present invention relates to a light emitting diode and a method of fabricating the same, and more particularly to a planar-type pleochroic light emitting diode allowing from a single chip a plurality of light emissions having different wavelengths.
2. Description of the Prior Art
As well known, a light emitting diode is far smaller in size than a gas laser or a solid laser, and thus is very suitable for a light source in optical communication. Accordingly, optical communication employing the light emitting diode as the light source has been actively studied.
In information transmission utilizing light as a medium, an optical multiplex transmission system has been proposed in order to increase the amount of information transmitted. In the system, a plurality of light emissions having different wavelengths and a plurality of light-guiding optical fibers are employed in one-to-one correspondence. Alternatively, the different-wavelength light emissions are introduced into and transmitted through a single optical fiber. If such a system is realized, optical communication with a very large information capacity is made possible in addition to the reduction in size of equipment and an increase in transmission rate. The latter technique requires the use of a diode as a light source which allows from a single chip a plurality of light emissions having different wavelengths. Such a diode is termed a pleochroic light emitting diode.
Most conventional light emitting diodes emit monochromatic light. A pleochroic light emitting diode having its structure as shown in FIG. 1 of the accompanying drawings has been proposed in Japanese Patent Publication No. 28869/70. The proposed diode comprises an n-type GaP substrate 1, a first p-type GaP region 2 formed by the diffusion of zinc from the substrate surface, and a second p-type GaP region 3 formed by the diffusion of zinc and oxygen from the substrate surface. Red and green lights are emitted from the first and second p-type regions 2 and 3 respectively. In this diode, however, only a small number of colors are available since different-wavelength light emissions are generated due to the diffusion of different kinds of impurities. Further, it is very difficult to diffuse the different impurities into their desired fine regions respectively. Therefore, this diode has not yet been widely used as a pleochroic light emitting diode.
Japanese Patent Application Laid-Open No. 99991/76 has proposed another pleochroic light emitting diode as shown in FIG. 2 of the accompanying drawings, in which a voltage is applied between an electrode P and each of rectangular-shaped electrodes N.sub.1, N.sub.2, N.sub.3, N.sub.4 and so on, and light emissions having different wavelengths are respectively taken out in the directions indicated by arrows L.sub.1, L.sub.2, L.sub.3, L.sub.4 and so on. However, since the proposed diode has a mesa structure and emits the lights from its side face, it encounters various problems that the process of fabricating the diode is complicated, that it is very difficult to make a satisfactory coupling between the diode and an optical fiber, and that the emitted lights are low in quantity. Therefore, it is difficult to put the diode into practical use. In FIG. 2, reference numerals 4, 5 and 6 indicate a p-type region, an n-type region and an SiO.sub.2 layer respectively.
The invention of the Japanese Patent Publication No. 28869/70 in which the different-wavelength light emissions are generated from the plural p-type regions formed on the n-type GaP substrate by the diffusion of different kinds of impurities, is different from the present invention in that different kinds of impurities are employed to obtain the different-wavelength light emissions.
The invention of the Japanese Patent Application Laid-Open No. 99991/76 in which an array of rectangular electrodes arranged on the same wafer are used and the respective regions are separated from each other by means of mesa etching techniques, is different from the present invention in that the diode has a mesa structure and the light emissions must be derived from a side face of the diode.